In the field of shelving assemblies, it is known to attach shelves and reinforcing crossbars to hollow posts by inserting hook portions on the shelves and crossbars into vertical slots in the posts. The slots are of a length sufficient to accept the entire hook portion, but once the hook portion is inside the post, only a limited part of the hook portion is actually disposed in the slot, leaving a large portion of the slot unoccupied, contributing to a looseness or abundance of "play" in the structure of assembled units. Once the shelves are loaded with books, equipment, or the like, the weight stabilizes the shelf hook portions in the post slots. However, the crossbars, which are intended to add to the structural stability of the assembled unit, are only loosely connected to the posts.
Thus, there is a need for an arrangement similar to the known arrangement described above, and therefore easy to assemble, but including means for stabilizing the interconnection of the crossbars and the posts.